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But Janeen Singer, the owner of Holy Sponges, hit back in an open letter to Dr. Gunter on her Instagram page.

She said: "When I first began using sponges, it changed my life. I spent over a year researching them and their history before I created the moon ritual kit. For me, it was a ritual to come back to my body after using tampons and being desensitized to my menstrual cycle."

She added: "I am by no means telling anyone what to put into their vagina, but I am offering an alternative that I have found to be incredibly reparative and positive."

Dr. Gunter said testing has revealed that sea sponges 'have bacteria and debris and they could introduce far more oxygen — a bad thing — into the vagina than a tampon or menstrual cup.'

She said: "According to the Food and Drug Administration, twelve "menstrual sponges" were tested at the University of Iowa in the 1980s and they and contained sand, grit, bacteria, and "various other materials."